Photodetection device and manufacturing method thereof

ABSTRACT

A photodetection device and a manufacturing method are provided. The photodetection device includes an absorption structure, a cathode, a charge multiplication region and an anode. The absorption structure is formed in a recess at a surface region of a semiconductor substrate, and configured to receive an incident light. The cathode is formed on a top surface of the absorption structure, and has a first conductive type. The charge multiplication layer is in lateral contact with the absorption structure, and is an intrinsic portion of the semiconductor substrate extending into the semiconductor substrate from a topmost surface of the semiconductor substrate. The anode is in lateral contact with the charge multiplication layer from a side of the charge multiplication region away from the absorption structure, and is a doped region in the semiconductor substrate having a second conductive type complementary to the first conductive type.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation application of and claims thepriority of a prior application Ser. No. 17/161,700, filed on Jan. 29,2021. The entirety of the above-mentioned patent application is herebyincorporated by reference herein and made a part of this specification.

BACKGROUND

Photodetection plays a key role in optical sensing and communicationapplications. A photodetection device, such as a photodiode, converts anoptical signal into an electric signal. The p-n junction in a photodiodeis typically reverse biased, thereby forming a relatively wide depletionregion. The current through the reverse-biased p-n junction will be afunction of the optically-generated electron-hole pairs. Carriersresulting from an electron-hole pair formation in the depletion regionare swept out by the electric field resulting from the reverse bias,thereby providing a rapid response.

With proper doping and reverse biasing, the carriers resulting from anelectron-hole formation cause impact ionization of other carriers in amultiplication region, a process denoted as avalanche breakdown.Photodiodes configured for such breakdown are denoted as avalanchephotodiodes. Because a single optically-induced carrier may produce manyadditional avalanche-ionized carriers, the resulting photocurrent gainmakes avalanche photodiodes very sensitive and high-speed opticaldetectors. However, the avalanche breakdown process is inherently noisy.The reverse bias may be raised to minimize the noise, but current gainof the avalanche photodiode may be compromised as a result of theincreased reverse bias.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1A is a schematic cross-sectional view illustrating aphotodetection device according to some embodiments of the presentdisclosure.

FIG. 1B is a schematic plan view illustrating the absorption structure,the charge layer, the charge multiplication regions and the anodes ofthe photodetection device as shown in FIG. 1A.

FIG. 2A is a schematic plan view illustrating a waveguide coupled to thephotodetection device according to some embodiments of the presentapplication.

FIG. 2B is a schematic three-dimensional view illustrating the waveguideand a portion of the photodetection device connected to the waveguide asshown in FIG. 2A.

FIG. 3 is a block diagram illustrating an optical receiver according tosome embodiments of the present application.

FIG. 4 is a flow diagram illustrating a manufacturing method for formingthe photodetection device 100 as shown in FIG. 1A, according to someembodiments of the present disclosure.

FIG. 5A through FIG. 5G are schematic cross-sectional views illustratingintermediate structures at various stages during the manufacturingprocess of the photodetection device as shown in FIG. 4 .

FIG. 6 is a schematic cross-sectional view of a photodetection deviceaccording to some embodiments of the present disclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

FIG. 1A is a schematic cross-sectional view illustrating aphotodetection device 100 according to some embodiments of the presentdisclosure.

Referring to FIG. 1A, the photodetection device 100 is an avalanchephotodiode. The photodetection device 100 is configured to receive alarge reverse bias voltage (near a breakdown voltage). In correspondingto incident light, electron-hole pairs may form in a light absorptionregion of the photodetection device 100, and carriers resulting fromformation of the electron-hole pairs may be accelerated by the strongelectrical field caused by the large reverse bias voltage, so as tocollide with and thereby ionize other atoms. Such collision results inadditional carriers, and these additional carrier are also acceleratedto release more carriers. This chain reaction may be referred as acharge multiplication process. Because a single optically-inducedcarrier may produce many additional avalanche-ionized carriers,sensitivity of the photodetection device 100 may be very high.

The photodetection device 100 may be formed on a surface region of asemiconductor substrate 102. In some embodiments, the semiconductorsubstrate 102 is a semiconductor-on-insulator (SOI) substrate. In theseembodiments, the semiconductor substrate 102 includes a backsemiconductor layer 104, a front semiconductor layer 106 and a buriedinsulating layer 108 sandwiched between the back semiconductor layer 104and the front semiconductor layer 106, and the photodetection device 100may be built in the front semiconductor layer 106. As an example, thesemiconductor substrate 102 may be a silicon-on-insulator wafer, and theback and front semiconductor layers 104, 106 may respectively includesilicon. On the other hand, the buried insulating layer 108 is formed ofan insulating material, such as silicon oxide.

The photodetection device 100 includes a cathode 110 and at least oneanode 112, and light absorption and charge multiplication may take placebetween the cathode 110 and the anode 112. A conductive type of thecathode 110 may be complementary to a conductive type of the anode 112.In some embodiments, the cathode 110 is P-type, while the anode 112 isN-type. During operation of the photodetection device 100, the cathode110 and the anode 112 are configured to receive a large reverse biasvoltage. For instance, the anode 112 of N-type is configured to receivea large positive voltage, while the cathode 110 of P-type is grounded orconfigured to receive a reference voltage. As a result of the reversebias voltage, the electrons generated during the charge multiplicationprocess may be drawn to the anode 112, while the holes generated duringthe charge multiplication process may be drawn to the cathode 112.Accordingly, current may be regarded as flowing from the anode 112 tothe cathode 110. In some embodiments, the photodetection device 100includes a cathode 110 and two anodes 112 at opposite sides of thecathode 110. In these embodiments, current may flow to the cathode 110from the two anodes 112 at opposite sides of the cathode 110. As will befurther described, the cathode may be a doped region formed in a cappinglayer deposited over the front semiconductor layer 106 of thesemiconductor substrate 102, while the anodes 112 may be doped regionsin the front semiconductor layer 106 of the semiconductor substrate 102.

In some embodiments, the photodetection device 100 has a separateabsorption charge and multiplication (SACM) design, such that the lightabsorption and the charge multiplication take place at different regionsof the photodetection device 100. In these embodiments, the lightabsorption may take place in an absorption structure 114 formed in arecess at a top surface of the front semiconductor layer 106. On theother hand, the charge multiplication may take place in portions of thesemiconductor substrate 102 (e.g., portions of the front semiconductorlayer 106 of the semiconductor substrate 102) at opposite sides of theabsorption structure 114, and these portions of the semiconductorsubstrate 102 (e.g., the portions of the front semiconductor layer 106)may be referred as charge multiplication regions 116. The absorptionstructure 114 may be an epitaxial structure, and may be formed of asemiconductor material with a bandgap lower than a bandgap of thesemiconductor material of the front semiconductor layer 106, in order toimprove the light absorption of the photodetection device 100. Forinstance, the front semiconductor layer 106 may be a silicon layer, andthe absorption structure 114 may be formed of germanium or a group III-Vsemiconductor material. In addition, the absorption structure 114 may bein contact with the cathode 110 from below the cathode 110. In otherwords, a top surface of the absorption structure 114 may be covered bythe cathode 110. In some embodiments, the absorption structure 114 mayprotrude from the top surface of the front semiconductor layer 106, suchthat a top portion of the absorption structure 114 is above the topsurface of the front semiconductor layer 106. On the other hand, therest portion of the absorption structure 114 is embedded in the frontsemiconductor layer 106, and in lateral contact (e.g., indirect lateralcontact) with the charge multiplication regions 116. In someembodiments, the absorption structure 114 slightly protrudes from thetop surface of the front semiconductor layer 106. For instance, a heightH_(114e) of the embedded portion of the absorption structure 114 may beabout 175 nm, and a height H_(114p) of the protruded portion of theabsorption structure 114 may be about 75 nm. Further, in someembodiments, the charge multiplication regions 116 are formed of anintrinsic semiconductor material. In those embodiments where the frontsemiconductor layer 106 is a silicon layer, the charge multiplicationregions 116 may be formed of intrinsic silicon. In addition, in someembodiments, the charge multiplication regions 116 respectively extendfrom a bottom surface of the front semiconductor layer 106 (i.e., a topsurface of the buried insulating layer 108) to the top surface of thefront semiconductor layer 106.

In some embodiments, a charge layer 118 is disposed between theabsorption structure 114 and the charge multiplication regions 116. Inthese embodiments, the charge multiplication regions 116 are in lateralcontact with the embedded portion of the absorption structure 114through the charge layer 118. A role of the charge layer 118 is tocontrol electric field inside the photodetection device 100.Specifically, an electric field in the absorption structure 114 shouldbe well below a breakdown field of the absorption structure 114, evenwhen the photodetection device 100 is biased near limit of its operation(i.e., breakdown in the charge multiplication regions 116). On the otherhand, the charge layer 118 is also functioned for ensuring a highelectric field in the charge multiplication regions 116. In someembodiments, the charge layer 118 is a P-type doped region in the frontsemiconductor layer 106, and the electric fields in the absorptionstructure 114 and the charge multiplication regions 116 may be tuned byaltering doping concentration of the charge layer 118. For instance, adoping concentration of the charge layer 118 may range from 10¹⁷ cm⁻³ to10¹⁹ cm⁻³. In addition, in these embodiments, the charge layer 118 mayextend to the top surface of the front semiconductor layer 106 from, forexample, the bottom surface of the front semiconductor layer 106 (i.e.,the top surface of the buried insulating layer 108), and the embeddedportion of the absorption structure 114 is located in a recess at a topsurface of the charge layer 118. Accordingly, opposite sidewalls of theembedded portion of the absorption structure 114 may be entirely coveredby the charge layer 118. As compared to an avalanche photodiode of whicha charge layer is a deep well with a top end distant from a top surfaceof a semiconductor substrate, the charge layer 118 has taller wallportions that are in lateral contact with the absorption structure 114from opposite sides of the absorption structure 114. Consequently, thecharge multiplication regions 116 in lateral contact with the absorptionstructure 114 through the charge layer 118 respectively has a largersurface (i.e., larger sidewall) in contact with the charge layer 118. Asa result, more carriers (e.g., electrons) may be swiped into the chargemultiplication regions 116 through such large contact surface, and amultiplication factor (also referred as gain) of the chargemultiplication taking place in the charge multiplication regions 116 canbe improved. Such improvement is particularly important when the reversebias voltage applied to the cathode 110 and the anodes 112 is raised tominimize noise accompany with the charge multiplication, since themultiplication factor is otherwise limited when the reverse bias voltageis increased. In those embodiments where the charge multiplicationregions 116 and the charge layer 118 both extend from the bottom surfaceto the top surface of the front semiconductor layer 106 of thesemiconductor substrate 102, a depth D₁₁₈ of the charge layer 118 and adepth D₁₁₆ of the charge multiplication regions 116 may be substantiallyequal to a thickness of the front semiconductor layer 106.

In some embodiments, exposed surfaces of the charge layer 118 and theabsorption structure 114 are covered by a capping layer 120. The exposedsurfaces of the charge layer 118 and the absorption structure 114 may bepassivated by the capping layer 120. In some embodiments, the cappinglayer 120 conformally covers the exposed surfaces of the charge layer118 and the absorption structure 114. The capping layer 120 may be asemiconductor layer, and the cathode 110 may be a doped region in thecapping layer 120. A top surface of the protruded portion of theabsorption structure 114 may be covered by the doped region of thecapping layer 120 (i.e., the cathode 110), while opposite sidewalls ofthe protruded portion of the absorption structure 114 as well as a topsurface of the charge layer 118 may be covered by rest portion of thecapping layer 120, which may be intrinsic. In some embodiments, thecapping layer 120 and the front semiconductor layer 106 are formed ofthe same semiconductor material, such as silicon. Further, in someembodiments, a thickness of the capping layer 120 ranges from 10 nm to100 nm.

In some embodiments, the anodes 112 are doped regions in the frontsemiconductor layer 106, and are laterally separated from the chargelayer 118 by the charge multiplication regions 116. A conductive type ofthe anodes 112 is complementary to the conductive type of the chargelayer 118 and the cathode 110. In those embodiments where the chargelayer 118 and the cathode 110 are P-type, the anodes 112 are N-type. Insome embodiments, each anode 112 has a heavily doped region 112 afunctioned as a contact area of the anode 112. Each heavily doped region112 a is formed in a shallow portion of the corresponding anode 112, andhas a doping concentration greater than a doping concentration of restportion of the anode 112. For instance, the doping concentration of theheavily doped region 112 a may range from 10¹⁹ cm⁻³ to 10²¹ cm⁻³, whilethe doping concentration of the rest portion of the anodes 112 may rangefrom 10¹⁷ cm⁻³ to 10¹⁹ cm⁻³. In some embodiments, the anodes 112 extendfrom the bottom surface of the front semiconductor layer 106 (i.e., thetop surface of the buried insulating layer 108) to the top surface ofthe front semiconductor layer 106. In those embodiments where the chargemultiplication regions 116 and the charge layer 118 also extend from thebottom surface to the top surface of the front semiconductor layer 106,a total depth D₁₁₂ of the anodes 112 may be substantially equal to thedepth D₁₁₆ of the charge multiplication regions 116 and the depth D 118of the charge layer 118, and each may be substantially equal to thethickness of the front semiconductor layer 106. Further, a depthD_(112a) of the heavily doped regions 112 a that is less than the totaldepth D 112 may range from 10 nm to 30 nm. In addition, in someembodiments, a trench TR is formed at a top surface of each anode 112(i.e., the top surface of the front semiconductor layer 106). The trenchTR may be disposed aside the heavily doped region 112 a, and an edge ofthe heavily doped region 112 a may be defined by a sidewall of thetrench TR. Further, the trench TR may be laterally spaced apart from thecharge layer 118 by a portion of the anode 112. In some embodiments, adepth D_(TR) of the trench TR is greater than the depth D_(112a) of theheavily doped regions 112 a, but less than a total depth D 112 of theanodes 112.

In some embodiments, the photodetection device 100 further includes acathode contact plug 122 and at least one anode contact plug 124. Thecathode 110 can be out routed through the cathode contact plug 122,while the at least one anode 112 can be out routed through the at leastone anode contact plug 124. The cathode contact plug 122 stands on thecathode 110, and electrically connects to the cathode 110. On the otherhand, the at least one anode contact plug 124 stands on the at least oneanode 112, and electrically connects to the at least one anode 112. Inthose embodiments where the photodetection device 100 has two anodes112, two anode contact plugs 124 are respectively disposed on one of theanodes 112. Further, the anode contact plugs 124 may be respectivelydisposed on the heavily doped region 112 a of one of the anodes 112. Insome embodiments, top surfaces of the cathode contact plug 122 and theanode contact plugs 124 are substantially coplanar with one another. Inthese embodiments, since the cathode contact plug 122 stands on thecathode 110 lying on the portion of the absorption structure 114protruded from the top surface of the semiconductor substrate 102 (e.g.,the top surface of the front semiconductor layer 106 of thesemiconductor substrate 102), the cathode contact plug 122 may beshorter than the anode contact plugs 124 that stand on the top surfaceof the semiconductor substrate 102 (e.g., the top surface of the frontsemiconductor layer 106 of the semiconductor substrate 102). The cathodecontact plug 122 and the anode contact plug(s) 124 are formed of aconductive material, such as tungsten, copper or the like.

In some embodiments, a dielectric layer 126 is formed on thesemiconductor substrate 102. The dielectric layer 126 may laterallysurround the cathode contact plug 122 and the anode contact plug(s) 124,and cover the top surface of the semiconductor substrate 102 (e.g., thetop surface of the front semiconductor layer 106 of the semiconductorsubstrate 102) as well as portions of the capping layer 120 notoverlapped with the cathode contact plug 122. In those embodiments wherethe trenches TR are formed at the top surfaces of the anodes 112, thetrenches TR may be filled by the dielectric layer 126. Further, in someembodiments, a top surface of the dielectric layer 126 is substantiallycoplanar with the top surfaces of the cathode contact plug 122 and theanode contact plug(s) 124. The dielectric layer 126 may be formed of adielectric material, such as silicon oxide, borophosphosilicate glass(BPSG), tetraethyl orthosilicate (TEOS), spin-on glass (SOG), undopedsilicate glass (USG), fluorosilicate glass (FSG), high-density plasma(HDP) oxide, plasma enhanced TEOS (PETEOS), the like or combinationsthereof.

FIG. 1B is a schematic plan view illustrating the absorption structure114, the charge layer 118, the charge multiplication regions 116 and theanodes 112 of the photodetection device 100 as shown in FIG. 1A. Itshould be noted that, the capping layer 120 (also the cathode 110therein) as well as the contact plugs (e.g., including the cathodecontact plug 122 and the anode contact plugs 124) are omitted in FIG.1B.

Referring to FIG. 1A and FIG. 1B, according to some embodiments, thecharge layer 118 is formed in line shape, and the absorption structure114 is filled in a trench defined at a top surface of the charge layer118 and extending along the charge layer 118 in line shape. In theseembodiments, at least one of the opposite ends of the absorptionstructure 114 in line shape may extend to a boundary of thephotodetection device 100, thus such end of the absorption structure 114can be functioned as an optical input of the photodetection device 100.As shown in FIG. 1B, both ends of the absorption structure 114 in lineshape extend to the boundary of the photodetection device 100. Further,the charge multiplication regions 116 and the anodes 112 at oppositesides of the charge layer 118 in line shape may extend along the chargelayer 118. In other words, the charge multiplication regions 116 and theanodes 112 may respectively be in line shape as well, and may extend tothe boundary of the photodetection device 100. In some embodiments, asshown in FIG. 1B, the heavily doped regions 112 a in the anodes 112 arerespectively formed in line shape extending along the anodes 112 also inline shape. In these embodiments, the heavily doped regions 112 a mayextend to the boundary of the photodetection device 100. In alternativeembodiments, the heavily doped regions 112 a may respectively be formedin patch shape (e.g., rectangular patch or circular patch), and may beat least partially surrounded by rest portions of the anodes 112.

Although not shown in FIG. 1B, the capping layer 120 may extend alongthe underlying charge layer 118 in line shape, and the cathode 110 as aportion of the capping layer 120 may extend along the absorptionstructure 114 formed in a trench at the top surface of the charge layer118. Accordingly, the cathode 110 as well as rest portions of thecapping layer 120 may respectively be formed in line shape. However,according to process and design requirements, the cathode 110 may beformed in other shapes, as long as the protruded portion of theabsorption structure 114 could be fully covered by the cathode 110 andthe rest portions of the capping layer 120.

FIG. 2A is a schematic plan view illustrating a waveguide 200 coupled tothe photodetection device 100 according to some embodiments of thepresent application. It should be noted that, the capping layer 120(also the cathode 110 therein) as well as the contact plugs (e.g.,including the cathode contact plug 122 and the anode contact plugs 124)are omitted in FIG. 1B.

Referring to FIG. 2A, a waveguide 200 may be optically coupled to theabsorption structure 114. In some embodiments, one of the opposite endsof the absorption structure 114 in line shape is in lateral contact withthe waveguide 200. Such end of the absorption structure 114 may beentirely in contact with the waveguide 200. Further, a portion of thecharge layer 118 covering sidewalls and a bottom surface of such end ofthe absorption structure 114 may be in lateral contact with thewaveguide 200 as well. In some embodiments, the waveguide 200 has a lineportion 200L and a divergent portion 200D. The waveguide 200 isconnected to the photodetection device 100 by a wide end of thedivergent portion 200D, and a narrow end of the divergent portion 200Dis connected to an end of the line portion 200L. A width of the lineportion 200L is substantially constant along an extension direction ofthe line portion 200L, while a width of the divergent portion 200Dgradually increases toward the photodetection device 100.

FIG. 2B is a schematic three-dimensional view illustrating the waveguide200 and a portion of the photodetection device 100 connected to thewaveguide 200.

Referring to FIG. 2A and FIG. 2B, in some embodiments, the waveguide 200is formed by shaping the front semiconductor layer 106 of thesemiconductor substrate 102. In these embodiments, the waveguide 200 isformed of the material of the front semiconductor layer 106 (e.g.,silicon), and a thickness of the waveguide 200 is substantiallyidentical with a thickness of the front semiconductor layer 106. Inaddition, the depth D₁₁₈ of the charge layer 118 may be substantiallyequal to the thickness of the waveguide 200, and a topmost surface ofthe charge layer 118 may be substantially coplanar with a top surface ofthe waveguide 200. Accordingly, a top surface of the portion of theabsorption structure 114 protruding from the topmost surface of thecharge layer 118 may be higher than the top surface of the waveguide200. Although not shown in FIG. 2B, the dielectric layer 126 asdescribed with reference to FIG. 1A may cover sidewalls and the topsurface of the waveguide 200, and the waveguide 200 may be wrapped bythe dielectric layer 126 and the buried insulating layer 108 of thesemiconductor substrate 102.

FIG. 3 is a block diagram illustrating an optical receiver 300 accordingto some embodiments of the present application.

Referring to FIG. 3 , the optical receiver 300 includes thephotodetection device 100 as described with reference to FIG. 1A andFIG. 1B. The photodetection device 100 is configured to receive a lightsignal LS provided through, for example, the waveguide 200 as describedwith reference to FIG. 2A and FIG. 2B, and is operated under a strongreverse bias. The light signal LS can be converted to a current signal,and output by the photodetection device 100. In some embodiments, thecurrent signal is output through the cathode 110 of the photodetectiondevice 100, which is described with reference to FIG. 1A. Atransimpedance amplifier (TIA) 302 is coupled to the output of thephotodetection device 100, and is configured to convert the currentsignal to a voltage signal of considerable magnitude. In someembodiments, the TIA 302 is a first block of a linear channel LC forprocessing the current signal. The linear channel LC may further includea filter 304 and an additional amplifier 306 coupled to an output of theTIA 302. The filter 304 is configured to shape the voltage signal fornoise reduction, and the additional amplifier 306 is configured to boostan output voltage of the TIA 302. Although the additional amplifier 306is depicted as coupled to an output of the filer 304, the additionalamplifier 306 may be alternatively coupled to the output of the TIA 302,while the filter 304 is coupled to an output of the additional amplifier306. In other embodiments, the filter 304 and the additional amplifier306 may be omitted. At an output of the linear channel LC, the providedoutput voltage can be later used by either signal processing or adecision circuit.

FIG. 4 is a flow diagram illustrating a manufacturing method for formingthe photodetection device 100 as shown in FIG. 1A, according to someembodiments of the present disclosure. FIG. 5A through FIG. 5G areschematic cross-sectional views illustrating intermediate structures atvarious stages during the manufacturing process of the photodetectiondevice 100 as shown in FIG. 4 .

Referring to FIG. 4 and FIG. 5A, step S400 is performed, and thetrenches TR are formed at the top surface of the semiconductor substrate102. The trenches TR extend into the front semiconductor layer 106 ofthe semiconductor substrate 102 from the top surface of the frontsemiconductor layer 106. In some embodiments, a method for forming thetrenches TR includes a lithography process and an etching process (e.g.,an anisotropic etching process).

Referring to FIG. 4 and FIG. 5B, step S402 is performed, and a chargeregion 518 as well as the anodes 112 are formed in the frontsemiconductor layer 106 of the semiconductor substrate 102. The chargeregion 518 will be patterned to form the charge layer 118 as describedwith reference to FIG. 1A and FIG. 1B. In some embodiments, a method forforming the charge region 518 includes a lithography process and an ionimplantation process. On the other hand, each anode 112 includes one ofthe heavily doped regions 112 a having a doping concentration greaterthan a doping concentration of rest portion of the anode 112. In someembodiments, a method for forming the anodes 112 includes a lithographyprocess and an ion implantation process for forming initial dopedregions having a relatively low doping concentration, and anotherlithography process as well as another ion implantation process forturning some portions of the initial doped regions into the heavilydoped regions 112 a. The heavily doped regions 112 a and rest portionsof the initial doped regions form the anodes 112. In some embodiments,the charge region 518 is formed before formation of the anodes 112. Inalternative embodiments, the charge region 518 is formed after formationof the anodes 112. Furthermore, portions of the front semiconductorlayer 106 between the anodes 112 and the charge region 518 form thecharge multiplication regions 116 as described with reference to FIG. 1Aand FIG. 1B.

Referring to FIG. 4 and FIG. 5C, step S404 is performed, and a recess RSis formed at a top surface of the charge region 518. The recess RS isconfigured to accommodate the absorption structure 114 to be formed inthe following step. In some embodiments, a method for forming the recessRS includes a lithography process and an etching process (e.g., ananisotropic etching process).

Referring to FIG. 4 and FIG. 5D, step S406 is performed, and theabsorption structure 114 is formed in the recess RS. In someembodiments, a method for forming the absorption structure 114 includesan epitaxial process. It should be noted that, although the absorptionstructure 114 is depicted as having a rectangular cross-section withfour right angles, the absorption structure 114 may be formed in othershapes, according to the epitaxial process and/or material selection forthe absorption structure 114.

Referring to FIG. 4 and FIG. 5E, step S408 is performed, and a cappingmaterial layer 520 is formed on the absorption structure 114 and thecharge layer 118. Exposed surfaces of the absorption structure 114 andthe charge layer 118 are covered by the capping material layer 520. Thecathode 110 described with reference to FIG. 1A will be formed in thecapping material layer 520, and the cathode 110 as well as rest portionof the capping material layer 520 may form the capping layer 120 asdescribed with reference to FIG. 1A. In some embodiments, a method forforming the capping material layer 520 includes forming a passivationlayer (not shown, such as silicon oxide or silicon nitride) on thecharge multiplication regions 116 and the anodes 112 by a depositionprocess, a lithography process and an etching process. Subsequently, thecapping material layer 520 is selectively formed on the exposed surfacesof the absorption structure 114 and the charge layer 118 by an epitaxialprocess. The passivation layer may be remained in the final structure.Alternatively, the passivation layer may be removed by an etchingprocess (e.g., an isotropic etching process). In other embodiments, amethod for forming the capping material layer 520 includes globallyforming a material layer on the structure shown in FIG. 5D by, forinstance, an epitaxial process. Subsequently, the material layer ispatterned to form the capping material layer 520 by a lithographyprocess and an etching process (e.g., an anisotropic etching process).

Referring to FIG. 4 and FIG. 5F, step S410 is performed, and the cathode110 is formed in the capping material layer 520. A portion of thecapping material layer 520 becomes the cathode 110, and the cathode 110as well as rest portion of the capping material layer 520 form thecapping layer 120 as described with reference to FIG. 1A. In someembodiments, a method for forming the cathode 110 includes a lithographyprocess and an ion implantation process.

Referring to FIG. 4 and FIG. 5G, step S412 is performed, and thedielectric layer 126 is globally formed on the current structure. Topsurfaces of the anodes 112, top surfaces of the charge multiplicationregions 116 and exposed surface of the capping layer 120 (including thecathode 110) are covered by the dielectric layer 126. Further, thetrenches TR may be filled up by the dielectric layer 126. In someembodiments, a method for forming the dielectric layer 126 includes adeposition process (e.g., a chemical vapor deposition (CVD) process),and may further include a planarization process. For instance, theplanarization process may include a polishing process, an etchingprocess or a combination thereof.

Referring to FIG. 4 and FIG. 1A, step S414 is performed, and the cathodecontact plug 122 as well as the anode contact plugs 124 are formed inthe dielectric layer 126. In some embodiments, a method for forming thecathode contact plug 122 and the anode contact plugs 124 includesforming through holes in the dielectric layer 126 by a lithographyprocess and an etching process (e.g., an anisotropic etching process).Subsequently, a conductive material is provided on the current structureby a deposition process (e.g., a physical vapor deposition (PVD)process), a plating process or a combination thereof. The conductivematerial may fill up the through holes in the dielectric layer 126, andmay further span on a top surface of the dielectric layer 126.Thereafter, portions of the conductive material above the dielectriclayer 126 may be removed by a planarization process, and remainedportions of the conductive material in the through holes form thecathode contact plug 122 and the anode contact plugs 124. For instance,the planarization process may include a polishing process, an etchingprocess or a combination thereof.

Up to here, the photodetection device 100 as shown in FIG. 1A has beenformed. The waveguide 200 as described with reference to FIG. 2A andFIG. 2B may be formed along with the photodetection device 100.Specifically, the waveguide 200 may be formed by patterning the frontsemiconductor layer 106 before formation of the dielectric layer 126. Inaddition, the structure including the photodetection device 100 (and thewaveguide 200) may be further subjected to a back-end-of-line (BEOL)process for forming metallization layers configured to out rout thecathode 110 and the anodes 112 of the photodetection device 100, as wellas a packaging process for forming a device die. In some embodiments, acircuit for driving the photodetection device 100 is integrated in thedevice die. In alternative embodiments, the driving circuit is formed inanother device die bonded to or electrically coupled to the device dieincluding the photodetection device 100.

FIG. 6 is a schematic cross-sectional view of a photodetection device100 a according to some embodiments of the present disclosure.

Referring to FIG. 1 and FIG. 6 , the photodetection device 100 a shownin FIG. 6 is similar to the photodetection device 100 as shown in FIG.1A, except that the trenches TR as shown in FIG. 1A may not be includedin the photodetection device 100 a as shown in FIG. 6 . In embodimentsshown in FIG. 6 , the anodes 112 may respectively have a substantiallyflat top surface.

As above, the absorption structure is disposed in a recess at a topsurface of the charge layer, and the charge layer is a doped region inthe semiconductor substrate extending into the semiconductor substratefrom a topmost surface of the semiconductor substrate. In addition, thecharge multiplication regions, which are intrinsic portions of thesemiconductor substrate extending into the semiconductor substrate fromthe topmost surface of the semiconductor substrate, are in lateralcontact with the charge layer from opposite sides of the charge layer.Since the charge layer and the charge multiplication regions both extendinto the semiconductor substrate from the topmost surface of thesemiconductor substrate, the charge layer may have a larger area inlateral contact with the absorption structure, and the chargemultiplication regions may respectively have a larger area in lateralcontact with the charge layer. Consequently, more carriers (e.g.,electrons) generated in the absorption structure can be swiped into thecharge multiplication regions through the charge layer. Therefore, amultiplication factor (also referred as gain) of the chargemultiplication taking place in the charge multiplication regions can beimproved, particularly when the reverse bias voltage applied to thecathode and anode(s) of the photodetection device is further raised.

In an aspect of the present disclosure, a photodetection device isprovided. The photodetection device comprises: an absorption structure,formed in a recess at a surface region of a semiconductor substrate, andconfigured to receive an incident light; a cathode, formed on a topsurface of the absorption structure, and having a first conductive type;a charge multiplication layer, in lateral contact with the absorptionstructure, and being an intrinsic portion of the semiconductor substrateextending into the semiconductor substrate from a topmost surface of thesemiconductor substrate; and an anode, in lateral contact with thecharge multiplication layer from a side of the charge multiplicationregion away from the absorption structure, and being a doped region inthe semiconductor substrate having a second conductive typecomplementary to the first conductive type.

In another aspect of the present disclosure, a photodetection device isprovided. The photodetection device comprises: a semiconductorsubstrate, comprising a back semiconductor layer, a front semiconductorlayer and a buried insulating layer sandwiched between the back andfront semiconductor layers, wherein the front semiconductor layer has arecess extending into the front semiconductor layer from a topmostsurface of the front semiconductor layer; an absorption structure,disposed in the recess, and configured to receive an incident light; acathode, lying on a top surface of the absorption structure, and has afirst conductive type; a charge multiplication region, being anintrinsic portion of the front semiconductor layer extending into thefront semiconductor layer from the topmost surface of the frontsemiconductor layer, and in lateral contact with the absorptionstructure; and an anode, being a doped region in the front semiconductorlayer extending into the front semiconductor layer from the topmostsurface of the front semiconductor layer, and in lateral contact withthe charge multiplication region from a side of the chargemultiplication region away from the absorption structure, wherein theanode has a second conductive type complementary to the first conductivetype.

In yet another aspect of the present disclosure, a photodetection deviceis provided. The photodetection device comprises: a light absorptionstructure, formed in a recess at a surface region of a semiconductorsubstrate; a cathode, lying on a top surface of the light absorptionstructure, and having a first conductive type; first and second chargemultiplication layers, in lateral contact with the light absorptionstructure from opposite sides of the light absorption structure, andbeing intrinsic portions of the semiconductor substrate extending intothe semiconductor substrate from a topmost surface of the semiconductorsubstrate; and first and second anodes, being doped regions in thesemiconductor substrate having a second conductive type complementary tothe first conductive type, wherein the first anode is in lateral contactwith the first charge multiplication region from a side of the firstcharge multiplication region away from the light absorption structure,and the second anode is in lateral contact with the second chargemultiplication region from a side of the second charge multiplicationregion away from the light absorption structure.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method for manufacturing a photodetectiondevice, comprising: performing an ion implantation process to form acharge region into a semiconductor substrate, wherein the charge regionhas a first conductive type; performing an ion implantation process toform an anode with a second conductive type into the semiconductorsubstrate, wherein the anode is laterally spaced apart from the chargeregion, and a portion of the semiconductor substrate in between thecharge region and the anode defines a charge multiplication region;forming a recess into the charge region, such that the charge region isshaped into a charge layer defining the recess; forming an absorptionstructure in the recess; forming a capping material layer covering theabsorption structure and the charge layer; and performing an ionimplantation process to form a cathode with the first conductive typeinto the capping material layer, wherein the cathode is in contact withthe absorption structure, and remained portions of the capping materiallayer define a capping layer entirely covering topmost surfaces of thecharge layer.
 2. The method for manufacturing the photodetection deviceaccording to claim 1, wherein the anode, the charge layer and theabsorption structure are each formed in a line shape, and aresubstantially parallel with one another.
 3. The method for manufacturingthe photodetection device according to claim 1, further comprising:patterning the semiconductor substrate to form a waveguide directly inlateral contact with the absorption structure.
 4. The method formanufacturing the photodetection device according to claim 3, whereinthe waveguide is directly in lateral contact with the charge layer aswell.
 5. The method for manufacturing the photodetection deviceaccording to claim 3, wherein the waveguide has a line portion and adivergent portion with a narrow end in contact with the line portion anda wide end in contact with the absorption structure and the chargelayer.
 6. The method for manufacturing the photodetection deviceaccording to claim 1, further comprising: forming a trench into thesemiconductor substrate before formation of the anode, wherein thetrench is positioned in a region of the semiconductor substrate to beformed with the anode.
 7. The method for manufacturing thephotodetection device according to claim 6, further comprising:performing an ion implantation process to form a heavily doped regioninto the anode, wherein the heavily doped region has the secondconductive type, and a sidewall of the heavily doped region is sharedwith the trench.
 8. The method for manufacturing the photodetectiondevice according to claim 1, wherein a method for forming the cappingmaterial layer comprises: forming a passivation layer covering thecharge multiplication region and the anode, while exposing the chargelayer and the absorption structure; and performing an epitaxial processto selectively grow a semiconductor material on the exposed charge layerand the exposed absorption structure, for forming the capping materiallayer.
 9. The method for manufacturing the photodetection deviceaccording to claim 1, further comprising: forming a dielectric layercovering the capping layer, the cathode, the charge multiplicationregion and the anode; and forming a first contact plug and a secondcontact plug through the dielectric layer, wherein the first contactplug is landed on the cathode, and the second contact plug is disposedon the anode.
 10. The method for manufacturing the photodetection deviceaccording to claim 9, wherein the dielectric layer is spaced apart fromthe charge layer via the capping layer.
 11. A method for manufacturing aphotodetection device, comprising: providing a semiconductor substratewith a front semiconductor layer, a back semiconductor layer and aburied insulating layer sandwiched between the front semiconductor layerand the back semiconductor layer; forming a charge region into the frontsemiconductor layer, wherein the charge region has a first conductivetype; forming an anode with a second conductive type into the frontsemiconductor layer, wherein the anode is laterally spaced apart fromthe charge region, and a portion of the front semiconductor layer inbetween the charge region and the anode defines a charge multiplicationregion; forming a recess into the charge region, such that the chargeregion is shaped into a charge layer defining the recess; forming anabsorption structure in the recess; forming a capping material layercovering the absorption structure and the charge layer; and forming acathode with the first conductive type into the capping material layer,wherein the cathode is in contact with the absorption structure, andremained portions of the capping material layer define a capping layerentirely covering topmost surfaces of the charge layer.
 12. The methodfor manufacturing the photodetection device according to claim 11,wherein the charge layer, the charge multiplication region and the anoderespectively span from a top surface of the front semiconductor layer toa top surface of the buried insulating layer.
 13. The method formanufacturing the photodetection device according to claim 11, furthercomprising: patterning the front semiconductor layer to form a waveguidedirectly in lateral contact with the absorption structure.
 14. Themethod for manufacturing the photodetection device according to claim13, wherein the waveguide is directly in lateral contact with the chargelayer as well.
 15. The method for manufacturing the photodetectiondevice according to claim 13, wherein the absorption structure, thecharge layer and the anode are each formed in a line shape, and theabsorption structure and the charge layer are respectively in lateralcontact with the waveguide by one end.
 16. A method for manufacturing aphotodetection device, comprising: performing an ion implantationprocess to form a charge region into a semiconductor substrate, whereinthe charge region has a first conductive type; performing an ionimplantation process to form anodes with a second conductive type intothe semiconductor substrate, wherein the anodes at opposite sides of thecharge region are laterally spaced apart from the charge region, andportions of the semiconductor substrate in between the charge region andthe anodes respectively define a charge multiplication region; forming arecess into the charge region, such that the charge region is shapedinto a charge layer defining the recess; forming an absorption structurein the recess; forming a capping material layer covering the absorptionstructure and the charge layer; and performing an ion implantationprocess to form a cathode with the first conductive type into thecapping material layer, wherein the cathode is in contact with theabsorption structure, and remained portions of the capping materiallayer define a capping layer entirely covering topmost surfaces of thecharge layer.
 17. The method for manufacturing the photodetection deviceaccording to claim 16, wherein the charge layer, the chargemultiplication regions and the anodes extends into the semiconductorsubstrate by an identical depth.
 18. The method for manufacturing thephotodetection device according to claim 16, further comprising:patterning the semiconductor substrate to form a waveguide directly inlateral contact with the absorption structure and the charge layer. 19.The method for manufacturing the photodetection device according toclaim 16, further comprising: forming a dielectric layer covering thecapping layer, the cathode, the charge multiplications region and theanodes; and forming a first contact plug and second contact plugsthrough the dielectric layer, wherein the first contact plug is landedon the cathode, and the second contact plugs are disposed on the anodes,respectively.
 20. The method for manufacturing the photodetection deviceaccording to claim 19, wherein the dielectric layer is spaced apart fromthe charge layer via the capping layer.